9
FN8112.1
May 17, 2006
BP: Block Protect Bit (Nonvolatile)
The Block Protect Bits BP determines which blocks of
the array are write protected. A write to a protected
block of memory is ignored. The block protect bit will
prevent write operations to half the array segment.
PUP1, PUP0: Power-up Bits (Nonvolatile)
The Power-up bits, PUP1 and PUP0, determine the
t
PURST
time delay. The nominal power-up times are
shown in the following table.
WD1, WD0: Watchdog Timer Bits
The bits WD1 and WD0 control the period of the
Watchdog Timer. The options are shown below.
Writing to the Control Registers
Changing any of the nonvolatile bits of the control and
trickle registers requires the following steps:
– Write a 02H to the Control Register to set the Write
Enable Latch (WEL). This is a volatile operation, so
there is no delay after the write. (Operation pre-
ceded by a start and ended with a stop).
– Write a 06H to the Control Register to set the
Register Write Enable Latch (RWEL) and the WEL
bit. This is also a volatile cycle. The zeros in the data
byte are required. (Operation proceeded by a start
and ended with a stop).
– Write a one byte value to the Control Register that
has all the control bits set to the desired state. The
Control register can be represented as qxy0 001r in
binary, where xy are the WD bits, and qr are the
power-up bits. This operation proceeded by a start
and ended with a stop bit. Since this is a nonvolatile
write cycle it will take up to 10ms to complete. The
RWEL bit is reset by this cycle and the sequence
must be repeated to change the nonvolatile bits
again. If bit 2 is set to ‘1’ in this third step (qxy0 011r)
then the RWEL bit is set, but the WD1, WD0, PUP1,
and PUP0, bits remain unchanged. Writing a second
byte to the control register is not allowed. Doing so
aborts the write operation and returns a NACK.
– A read operation occurring between any of the previ-
ous operations will not interrupt the register write
operation.
– The RWEL bit cannot be reset without writing to the
nonvolatile control bits in the control register, power
cycling the device or attempting a write to a write
protected block.
To illustrate, a sequence of writes to the device con-
sisting of [02H, 06H, 02H] will reset all of the nonvola-
tile bits in the Control Register to 0. A sequence of
[02H, 06H, 06H] will leave the nonvolatile bits
unchanged and the RWEL bit remains set.
Note: 1. t
PURST
is set to 200ms as factory default.
2. Watchdog timer bits are shipped disabled.
Fault Detection Register (FDR)
The Fault Detection Register provides the user the
status of what causes the system reset active. The
Manual Reset Fail, Watchdog Timer Fail and Three
Low Voltage Fail bits are volatile.
The FDR is accessed with a special preamble in the
slave byte (1011) and is located at address 0FFh. It
can only be modified by performing a byte write opera-
tion directly to the address of the register and only one
data byte is allowed for each register write operation.
There is no need to set the WEL or RWEL in the con-
trol register to access this fault detection register.
BP
Protected Addresses
(Size)
Memory
Array Lock
0 None None
1 100h - 1FFh (256 bytes) Upper Half of
Memory Array
PUP1 PUP0 Power-on Reset Delay (t
PURST
)
0 0 50ms
0 1 200ms (default)
1 0 400ms
1 1 800ms
WD1 WD0 Watchdog Time Out Period
0 0 1.4 seconds
0 1 200 milliseconds
1 0 25 milliseconds
1 1 disabled (factory default)
7 6543210
LV1F LV2F 0 WDF MRF 0 0 0
X40020, 40021
